Genotype


Genotype
Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal colour in pea. The letters B and b represent genes for colour and the pictures show the resultant flowers.

The genotype is the genetic makeup of a cell, an organism, or an individual (i.e. the specific allele makeup of the individual) usually with reference to a specific character under consideration.[1] For instance, the human CFTR gene, which encodes a protein that transports chloride ions across cell membranes, can be dominant (A) as the normal version of the gene, or recessive (a) as a mutated version of the gene. Individuals receiving two recessive alleles will be diagnosed with Cystic fibrosis. It is generally accepted that inherited genotype, transmitted epigenetic factors, and non-hereditary environmental variation contribute to the phenotype of an individual.

Non-hereditary DNA mutations are not classically understood as representing the individual's genotype. Hence, scientists and physicians sometimes talk for example about the (geno)type of a particular cancer, that is the genotype of the disease as distinct from the diseased.

Contents

Genotype and genomic sequence

One's genotype differs subtly from one's genomic sequence. A sequence is an absolute measure of base composition of an individual, or a representative of a species or group; a genotype typically implies a measurement of how an individual differs or is specialized within a group of individuals or a species. So typically, one refers to an individual's genotype with regard to a particular gene of interest and, in polyploid individuals, it refers to what combination of alleles the individual carries (see homozygous, heterozygous). The genetic constitution of an organism is referred to as its genotype, such as the letters Bb. (B - dominant genotype and b - recessive genotype)

Genotype and Mendelian inheritance

The distinction between genotype and phenotype is commonly experienced when studying family patterns for certain hereditary diseases or conditions, for example, haemophilia. Due to the diploidy of humans (and most animals), there are two alleles for any given gene. These alleles can be the same (homozygous) or different (heterozygous), depending on the individual (see zygote). With a dominant allele, the offspring is guaranteed to inherit the trait in question irrespective of the second allele.

In the case of an albino with a recessive allele (aa), the phenotype depends upon the other allele (Aa, aA or AA). An affected person mating with a heterozygous individual (Aa or aA, also carrier) there is a 50-50 chance the offspring will be albino's phenotype. If a heterozygote mates with another heterozygote, there is 75% chance passing the gene on and only a 25% chance that the gene will be displayed. A homozygous dominant (AA) individual has a normal phenotype and no risk of abnormal offspring. A homozygous recessive individual has an abnormal phenotype and is guaranteed to pass the abnormal gene onto offspring.

In the case of haemophilia, it is sex-linked thus only carried on the X chromosome. Only females can be a carrier in which the abnormality is not displayed. This woman has a normal phenotype, but runs a 50-50 chance, with an unaffected partner, of passing her abnormal gene on to her offspring. If she mated with a man with hemophilia (another carrier) there would be a 75% chance of passing on the gene.

Genotype and mathematics

Main articles: Genetic programming and evolutionary algorithm

Inspired by the biological concept and usefulness of genotypes, computer science employs simulated phenotypes in genetic programming and evolutionary algorithms. Such techniques can help evolve mathematical solutions to certain types of otherwise difficult problems.

Determining genotype

Genotyping is the process of elucidating the genotype of an individual with a biological assay. Also known as a genotypic assay, techniques include PCR, DNA fragment analysis, allele specific oligonucleotide (ASO) probes, DNA sequencing, and nucleic acid hybridization to DNA microarrays or beads. Several common genotyping techniques include restriction fragment length polymorphism (RFLP), terminal restriction fragment length polymorphism (t-RFLP),[2] amplified fragment length polymorphism (AFLP),[3] and multiplex ligation-dependent probe amplification (MLPA).[4]

DNA fragment analysis can also be used to determine such disease causing genetics aberrations as microsatellite instability (MSI),[5] trisomy[6] or aneuploidy, and loss of heterozygosity (LOH).[7] MSI and LOH in particular have been associated with cancer cell genotypes for colon, breast and cervical cancer.

The most common chromosomal aneuploidy is a trisomy of chromosome 21 which manifests itself as Down syndrome. Current technological limitations typically allow only a fraction of an individual’s genotype to be determined efficiently.

References

External links


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Look at other dictionaries:

  • Genotype — Génotype Une molécule d ADN : les deux brins sont composés de nucléotides, dont la séquence constitue l information génétique. Le génotype est l ensemble ou une partie donnée de la composition génétique (information génétique) d un… …   Wikipédia en Français

  • génotype — [ ʒenotip ] n. m. • 1930; all. Genotypus, de Gen « gène » et Typus « type » ♦ Biol. Patrimoine génétique d un individu dépendant des gènes hérités de ses parents, qu ils soient exprimés ou non (opposé à phénotype). Les vrais jumeaux ont le même… …   Encyclopédie Universelle

  • genotype — gen o*type n. (Genetics) A group of organisms sharing a specific genetic constitution. [WordNet sense 1] [WordNet 1.5] 2. (Genetics) The genetic constitution of an organism, specifying the particular alleles at defined loci in the genome; used… …   The Collaborative International Dictionary of English

  • genotype — genotype. См. генотип. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • genotype — genetic constitution of an individual, 1910, from Ger. Genotypus (1909); see GENE (Cf. gene) + TYPE (Cf. type). Earlier the same word was used with a sense of type species of a genus (1897); in this case, the first element is from GENUS (Cf.… …   Etymology dictionary

  • genotype —  Genotype  Генотип   Совокупность генов организма. Термин «генотип» предложен В.Иоганзеном в 1909 …   Толковый англо-русский словарь по нанотехнологии. - М.

  • genotype — ► NOUN Biology ▪ the genetic constitution of an individual organism. Often contrasted with PHENOTYPE(Cf. ↑phenotype). DERIVATIVES genotypic adjective …   English terms dictionary

  • genotype — [jen′ə tīp΄, jē′nətīp΄] n. [< Gr genos, race, kind (see GENUS) + TYPE] 1. the fundamental constitution of an organism in terms of its hereditary factors 2. a group of organisms each having the same hereditary characteristics 3. the type… …   English World dictionary

  • Génotype — Une molécule d ADN : les deux brins sont composés de nucléotides, dont la séquence constitue l information génétique. Le génotype est l ensemble ou une partie donnée de la composition génétique (information génétique) d un individu[1]. Le… …   Wikipédia en Français

  • genotype — genotypic /jen euh tip ik, jee neuh /, genotypical, adj. genotypically, adv. /jen euh tuyp , jee neuh /, n. Genetics. 1. the genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex …   Universalium